Uglify SyntaxError: Unexpected token: punc ())

I am trying to use gulp in order to minify a folder containing JS files. However, one of the files has the above error, preventing it from being minified.

I managed to catch and print the error, which I've partially printed here:

JS_Parse_Error {
 message: 'SyntaxError: Unexpected token: punc ())',
 filename: 'ex.js',
 line: 189,
 col: 25,
 pos: 6482,
 stack: Error\n    at new JS_Parse_Error (eval at <anonymous> ... ) 
 plugin: 'gulp-uglify',
 fileName: '.../js/ex.js',
 showStack: false

The file in question contains the following, shortened:

function() {
    buttons: {
        confirm: function() {
            $.post('/ajax-handler', {
                .done( function(response) {
                    var data = filterResponse(response);
                    if (data['status'] == 'success') {
                        sleep(1000).then(() => {
                    *       ...
                        sleep(5000).then(() => {

                    } else {
                .fail( function(err, status, response) {
        cancel: function() {}

I added the "*" above in order to indicate the exact position listed by JS_Parse_Error.



// Update

From the comments ~ @imolit

 v2.0.0 (2018-09-14) - BREAKING CHANGES (link)

Switch back to uglify-js (uglify-es is abandoned, if you need uglify ES6 code please use terser-webpack-plugin).

Original answer before the update...

I hope you can get inspired by this solution which works with webpack. (link below)

Simply teach UglifyJS ES6

There are two versions of UglifyJS - ES5 and ES6 (Harmony), see on git
ES5 version comes by default with all the plugins, but if you install a Harmony version explicitly, those plugins will use it instead.


"uglify-js": "git+"


npm install --save [email protected]:mishoo/UglifyJS2#harmony

yarn add git:// --dev


To use it with webpack install also the webpack plugin

npm install uglifyjs-webpack-plugin --save-dev

yarn add uglifyjs-webpack-plugin --dev

then import the manually installed plugin

var UglifyJSPlugin = require('uglifyjs-webpack-plugin');

and replace it in code

-  new webpack.optimize.UglifyJsPlugin({ ... })
+  new UglifyJSPlugin({ ... })

For more webpack info (Installation/Usage) see


npm install uglifyjs-webpack-plugin --save-dev is not enough

The main problem is "uglifyjs-webpack-plugin": "^0.4.6" in webpack's package.json

According to semver, ^0.4.6 := >=0.4.6 <0.5.0. Because of the leading zero, webpack will never use the 1.0.0-beta.2.

So after running npm i -D [email protected], you need to do one more step which is rm -rf node_modules/webpack/node_modules/uglifyjs-webpack-plugin. Then webpack will pick up the version from node_modules/uglifyjs-webpack-plugin instead of node_modules/webpack/node_modules/uglifyjs-webpack-plugin

Update on 2018-04-18: webpack v4 does not have this issue


Add the babel-preset-es2015 dependency to fix this.

And also add 'es2015' in .babelrc file.

    "presets": ["es2015"]

I am having the same issue, i found a great answers here that helped me to reach the the file that was causing the error.

Go to Rails Console and Paste:

JS_PATH = "app/assets/javascripts/**/*.js";
Dir[JS_PATH].each do |file_name|
  puts "\n#{file_name}"
  puts Uglifier.compile(

Hope it helps someone!


If you got this error using Grunt (grunt-contrib-uglify) the solution is to install ES6 version of the plugin:

npm install grunt-contrib-uglify-es --save-dev

For me it had nothing to do with Uglify not working correctly, but rather a dependency (in this case empty-promise) that has not been compiled to ES5 yet. As we just imported the raw source file, but babel is only transpiling files outside of node_modules, uglify got confused by the ES6 syntax.

Simply check if any dependency you've recently added might not have a "dist" build.


Add stage-3 to presets in .babelrc file.

  "presets": [

I had the same problem with you. I was using gulp.js. I solved this problem thanks to js files change ES format. For example before solved is my code:

for (district for response) {
                $('#districts').append('<option value="' + + '">' + + '</option>');

after fix code:

for (district in response) {
                $('#districts').append('<option value="' + + '">' + + '</option>');

In summary, the problem is due to Ecma-uglify.js.


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